Wren day also known as Wren's Day, Day of the Wren, or Hunt the Wren Day (Irish: Lá an Dreoilín) is celebrated on 26 December, St. Stephen's Day. The tradition consists of "hunting" a fake wren, and putting it on top of a decorated pole. Then the crowds of mummers or strawboys celebrate the wren (also pronounced as the wran) by dressing up in masks, straw suits and colourful motley clothing and, accompanied by traditional céilí music bands, parade through the towns and villages. These crowds are sometimes called wrenboys.
In past times, and into the 20th century, an actual bird was hunted by wrenboys on St. Stephen's Day. The captured wren was tied to the wrenboy leader's staff pole. The captured wren would be kept alive as the popular mummers' parade song states "A penny or tuppence would do it no harm". The song, of which there are many variations, asked for donations from the townspeople. Often, the boys gave a feather from the bird to patrons for good luck. The money was used to host a dance for the town, held that night. The pole, decorated with ribbons, wreaths and flowers, as well as the wren, was the centre of the dance. Over time, the live bird was replaced with a fake one that is hidden, rather than chased. The band of young boys has expanded to include girls, and adults often join in. The money that is collected from the townspeople is usually donated to a school or charity. A celebration is still held around the decorated pole.
It is theorised that the wren celebration has descended from Celtic mythology. Ultimately, the origin may be a Samhain or midwinter sacrifice and/or celebration, as Celtic mythology considered the wren a symbol of the past year (the European wren is known for its habit of singing even in mid-winter, and sometimes explicitly called "winter wren"); Celtic names of the wren (draouennig, drean, dreathan, dryw etc.) also suggest an association with druidic rituals. The tradition may also have been influenced by Scandinavian settlers during the Viking invasions of the 8th to 10th centuries. Various associated legends exist, such as a wren being responsible for betraying Irish soldiers who fought the Viking invaders by beating its wings on their shields, in the late 1st and early 2nd millennia, and for betraying the Christian martyr Saint Stephen, after whom the day is named. This mythological association with treachery is a possible reason why the bird was hunted by wrenboys on St. Stephen's Day, and/or why a pagan sacrificial tradition was continued in Christian times. Despite the abandonment of the wren killing practice, devoted wrenboys continue to ensure that the Gaelic tradition of celebrating the wren continues although it is no longer widespread.
Similar traditions of hunting the wren have been performed on the Isle of Man on Boxing Day and in Pembrokeshire, Wales on Twelfth Day (6 January) and, on the first Sunday of December in parts of Southern France, including Carcassonne.  The custom has been revived in Suffolk, by Pete Jennings and the Old Glory Molly Dancers and has been performed in the village of Middleton, every Boxing Day evening since 1994.
In Galicia, Spain, the Caceria del rey Charlo (Chase of King Charles) was performed. The inhabitants of Vilanova de Lourenza would chase down a wren and, after tying it to a pole, would parade it and show it to the abbot of the local monastery, who would proceed then to offer them food and drink and appoint two leaders of local town council out of the four candidates proposed by the neighbours. This tradition has been recorded since the 16th century. The sources are somewhat misleading about the date, since they claim it was "New Year`s Day" but it might mean "The day after Christmas", which was regarded back then to signal the end of the year.
In 1955 Liam Clancy recorded "The Wran Song" ("The Wren Song"), which was sung in Ireland by wrenboys. In 1972 Steeleye Span recorded "The King" on Please to See the King, which is along similar lines. They made another version, "The Cutty Wren", on their album Time. "Hunting the Wren" is on John Kirkpatrick's album Wassail!. The Chieftains made a collection of wrenboy tunes on The Bells of Dublin. In the song "The Boys of Barr na Sráide", which is based on a poem by Sigerson Clifford, the wren hunt also plays a prominent part.
"The Wren [Wran] Song" is also on the Clancy Brothers and Tommy Makem's 1995 album Ain't it Grand Boys: A Collection of Unissued Gems, as the last song in "Children's Medley". The spoken introduction tells how as boys they would go out on Christmas Day and kill a wren, and on the next day, St. Stephen's Day, they would go from house to house singing this song and asking for money "to bury the wren".
- "Christmas and New Year in Ireland Long Ago".
- The British and European symbolic hunting of the Eurasian Wren is investigated by Elizabeth Atwood Lawrence, Hunting the Wren: Transformation of Bird to Symbol (University of Tennessee) 1997.
- Something for everybody (and a garland for the year) by John Timbs, 1861. pp. 152-155
- The Golden Bough by James George Frazer, NuVision Publications, LLC, 2006, ISBN 1-59547-959-7, ISBN 978-1-59547-959-4. pp.294-295
- "old Glory & The Cutty Wren" by Pete Jennings.
- "La cacería del reyezuelo: análisis de una cacería ancestral en los países célticos" by Fernando Alonso Romero at Anuario Brigantino, issue 24, 2001
- "Ain't it Grand Boys: A Collection of Unissued Gems", the Clancy Brothers and Tommy Makem, Columbia Records, 1995. Children's Medley, ibid.
- Archived audio recording of The Wren Song, sung by Will Murphy, Colliers, Newfoundland
- Discussions about the Wren song
- Recording of the Wren dance/song on the Isle of Man
- Handbook of Birds of the World: Wrens family account
- Hunting the Wren on the Dingle peninsula - An excellent account of the origins, history, contemporary aspects and international connections of the Wren.
- Hunt the wren in the Isle of Man
- The Weird Side of St. Stephen's day in Ireland & Elsewhere (Fustar.info)
- Wren Boy Festival
- Wren Day
- Traditional Customs for Wren Day